furnace to the holding furnace at a casting cell without pumping or tapping, which avoids turbulent transfers. Another progressive way to avoid transfer troubles is to eliminate the large central melting furnace and instead operate a smaller electric melting and holding furnace at each casting cell. Eliminating a central gas-fired melting furnace eliminates transfer ladles, the ladle preheat station, fork trucks and the danger of hauling molten metal around the casting facility, as well as emissions associated with a large furnace. Te only molten metal transfer required is from the furnace to the mold.
Justify the Expense Unfortunately, most metalcasters
don’t have the luxury to start fresh when it comes to engineering their melting and holding operations, but they can take steps toward better efficiency through smart planning. When any changes or improve-
ments are planned for a casting cell, consider what can be done to incor- porate in-cell melting and holding or other furnace upgrades then or in the future. Furnaces can be rebuilt or retrofitted, and spending more during relining for better insulation is a good way to gain efficiency. Adding to capacity with an additional or larger furnace in a central melting house isn’t much of a change, but adding a furnace to a casting cell requires engi- neering evaluation. Metalcasters should consider the
total operating costs affected by furnace choice before making the investment. For instance, in operations with a central melting area, ingates and risers are often left to cool to room tempera- ture before they are taken to the central furnace area to be remelted, requiring more energy than if they were used to charge the furnace while still hot. Tis extra energy cost should be factored in when determining your ROI. Also remember, the most efficient
furnace available may not yield a suitable ROI if you don’t melt enough metal on a day-to-day basis to justify the expense. A couple of years ago, the Ohio
Department of Energy gave out substantial energy grants to allow facilities to experiment with ways to gain theoretical energy efficiencies. At one facility, the project examined the extreme efficiency achievable in an electric furnace. Te study found the best efficiency possible was 78%, but the equipment needed to reach that rate had an ROI of more than 18 years. Te best energy efficient furnace available industry-wide at that point yielded 74%-75% efficiency via electric melting and had an ROI of two years. With a large range of available
electric furnaces achieving 70% efficiency, aluminum metalcasters may find that switching to a more efficient furnace is worth the investment, but proper calculation of total costs will prevent overspending.
August 2013 MODERN CASTING | 29
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